This invention relates to single-pass ink jet printing. In many instances, it is desirable to print images on a continuously moving object such as a package carried on a conveyor, or on a web or a sheet of substrate in a single pass, i.e., without requiring any repeated or return motion of the ink jet head with respect to the object. The spacing of ink jet orifices in an ink jet printer in a row extending across the width of the substrate, however, normally does not provide high enough resolution to produce an acceptable image. Moreover, in many cases it is desirable to be able to change the color of the ink used in printing without replacing the printhead but conventional printers are not usually capable of permitting printing of different colored inks from the same printhead.
In general, in one aspect, the invention features a method of single pass printing. A single pass ink jet print head has an array of ink jet orifices arranged transversely to a substrate which moves relative to the print head during printing. A pump supplies ink from an ink reservoir to the print head. UV curable ink is provided in the reservoir. Ink is jetted through the orifices to print on the substrate. The UV-curable ink is circulated through the print head when jetting and when not jetting.
Implementations of the invention may include one or more of the following features.
The ink jet head may include an ink inlet through which ink is supplied and an ink outlet through which ink is removed from the ink jet head. The reservoir may be positioned remotely from the print head and the ink may be directed from the outlet to the reservoir. Ink pressure may be controlled downstream of the reservoir, e.g., by a J-tube, so that a negative pressure is maintained at the ink jet orifices when the orifices are not jetting. The head may include ink jet modules extending transversely to the direction of the motion of the substrate. The modules may overlap and communicate with a manifold which distributes ink from the inlet to each of the modules. The head may have a print width of about 5.5 inches or more or about 10 inches and a resolution of about 275 dots per inch or more or about 600 dots per inch. The ink may be filtered at the ink outlet or the ink inlet. The jetting may be effected by piezoelectric transduction. The ink at the head may be maintained at a substantially uniform temperature.
Other features and advantages of the invention will become apparent from the following description and from the claims.